This invention relates to a method for producing a color filter and more particularly to a method for producing a color filter convenient to be employed as a color liquid crystal display device.
Up to now, color filters in general have been produced by a dyeing method, a printing method or a pigment dispersion method, in which a transparent substrate is dyed using a binder containing a dye or a pigment.
However, since the dyeing method is a method for selectively dyeing a thin resin film on a substrate with a dyestuff, it is necessary to carry out the resist printing process and the photolithographic process each time the color is changed, such that the process becomes complex with consequential rise in production costs. On the other hand, since the dyestuff is employed as a coloring agent, the product is poor in thermal resistance, weatherability or resistance against chemicals. Although there is no necessity of carrying out the resist printing process with the above printing method, there is a limitation imposed on refinement of color patterns, such that, the more variegated the color pattern, the precision of the printing position becomes the worse. Although it is possible to generate fine patterns with the pigment dispersion method, the photolithographic process of high precision needs to be carried out each time the color is changed, thus complicating the process.
On the other hand, there has been proposed a method for producing a color filter by an electrodeposition coating method. For example, with the electrodeposition method for preparation of the color filter, in which a transparent electrode is previously formed with a pre-set pattern and placed in a vat containing an ionized high molecular material containing a dye or a pigment dissolved or dispersed in a solvent, and in which a color filter is produced under application of an electrical voltage, a transparent electrode for the formation of the color filter is required in addition to the transparent display electrode. Since the transparent electrode needs to be insulated from one color to another, an etching process is required, while there is a risk of the decreased yield due to line defects produced by electrical shorting. Besides, since respective pixels need to be electrically coupled to one another, there is imposed a limitation on pixel arraying.
In the Japanese Laid-Open Patent Application No.61-203403, there is disclosed a method for producing a color filter by peeling a photosensitive coating film on an electrode in a pattern by a photolithographic process, effecting electrodeposition coating on an exposed portion of the electrode surface, and peeling the photosensitive coating film of a neighboring region followed by electrodeposition. In the Japanese Laid-Open Patent Application No.61-272720, there is disclosed a method for producing a color filter by forming a positive photosensitive coating film on an electrically conductive layer, exposing and developing the coating and electrodepositing the developed coating on the exposed portion. In the Japanese Laid-Open Patent Application No.61-279803, there is disclosed a method for producing a color filter by exposing and developing a positive photosensitive resin layer on a transparent electrode in a mosaic pattern for effecting the electrodeposition followed by forming another neighboring mosaic pattern and effecting electrodeposition. The production process is complicated with these methods since the colored layers need to be formed by a process of light irradiation and development from one color to another.
There has recently been proposed in Japanese Laid-Open Patent Application No.4-287003 a method consisting in forming patterns different in at least three stages on a photosensitive coating film formed on a transparent electrically conductive layer by one step of light irradiation and sequentially repeating the steps of development and formation of colored layers. This method has an advantage that, since the pattern can be formed by one light irradiation step, the process may be simplified and the number of expensive light irradiation units may be decreased while there is no necessity of precise registration for pattern formation as compared to the photolithographic process in which the colored layers are formed separately from color to color. Although the method of forming the entire pattern required of the color filter by one light irradiation operation is excellent as the method per se, there may be occasions in which the conditions of light exposure and development become more severe than with the conventional method of repeating the light irradiation and development from color to color. In such case, the photosensitive coating film tends to be lowered in durability while there is a risk of deterioration in pattern precision.
For resolving such deficiency, there is proposed a method consisting in forming a light shielding layer in need of utmost precision using a first photosensitive coating film and forming patterns for other colored layers by sole light irradiation as described above. There is also proposed a method consisting of carrying out the light exposure for pattern formation by two steps and re-forming the second photosensitive coating film in need of durability to meet with light irradiation. These methods are meritorious in that the production process is simplified as compared to the photolithographic process in which the colored layers are formed from color to color. However, since at least two photosensitive coating films need to be formed, material costs are increased as compared to the method of using a sole photosensitive coating film. With the method for producing a color filter in which the photosensitive resin constituting the photosensitive coating film accounts for a major portion of material costs and is coated by electrodeposition coating which substantially inhibits reutilization of the coating material, the problem of material costs is crucial in industrial production and in need of improvement along with process simplification.